The oyerajl^objective Of this project is to determine the physiological relevance of the NKG2D receptor in NK cell^mediated land T cellr^mediatcid immune responses. In prior studies, we have implicated this receptor in NK cell-mediated anti-viral and anti-tumor immunity, and have uncovered an important role for NKG2D in the pathology associated with type I autoimmune diabetes. In this program, we will focus our efforts towards defining the mechanisms of NKG2D-dependent activation of T cells and NK cells in model systems of immunity to tumors and pathogens and in autoimmunity. Specific aims are: 1. To determine the mechanisms whereby'Nk<32D and its ligands contribute to autoimmune diabetes in the NOD and EAE mouse model; 2. To;deplop genetic models for selective deficiency of NKG2D in discrete cell lineages and to determine the effectS;pn innate and adaptive immune responses; and, 3. To test the hypothesis that NKG2D costimulation in: human and mouse T cells is restricted to unique T cell subsets or activation states. Aim 1 will evaluate the potiB'ntial role for NKG2D in models of autoimmunity that are regulated by NK cells, CD8+ cells, and CD4+ T cells In addition, we will test whether anti-NKG2D mAb treatment can affect autoimmune manifestations othel' than diabetes. In aim 2 we will generate a conditionally NKG2D-deficient mouse on the C57BU6 bacltground in order to test the hypothesis that NKG2b is important in immunity against autoantigens, tumors and pathogens. An important goal is to determine in model systems where the function of NKG2D is critical -whether NKG2D is required in NK cells, T cells, or both cell types. Specific aim 3 will determine why NKG2D is unable to costimulate freshly isolated human NKG2D-- T cells or short-term activated mouse NKG2D+ T cells, but is able to efficiently costimulate long-term cultured human and mouse CD8+ T cells and clones, as well as CD8+ T cells isolated from tissue undergoing an autoimmune reaction in vivo. RELEVANCE (See Instructions): NKG2D has been demonstrated to provide protective immunity against pathogens and tumors, as well as implicated in autoimmune diseases, including rheumatoid arthritis and type I diabetes. A better understanding of this immune receptor and its ligands may provide new therapeutic approaches for vaccination against tumors and microbial pathogens and for intervention in autoimmune diseases.